1. Field of the Invention
The present invention relates to power transfer devices and, more specifically, to a wireless power transfer device.
2. Description of the Related Art
Wireless power transfer devices can be used to transfer power from a source to a load without requiring a wired connection between the two. They can also be used to transfer data wirelessly as well. Such devices are commonly used in situations where it is either impractical to use wired connections or potentially unsafe to do so. For example, many electric tooth brush systems use wireless power transfer to recharge the batteries in the tooth brush. Since the elements of the system are covered in non-conductive plastic, there is little chance of electric shock with such systems.
Modern digital devices, such as smart phones, tablets and the like, require frequent recharging. However, most such systems require the digital device to be plugged into a recharger. Because doing so is somewhat inconvenient, users often forget to recharge their devices.
Numerous wireless power transfer methods have been proposed and studied in the past for various applications. Specifically, wireless power transfer has been achieved using near-field coupling in several applications such as, RFID tags, telemetry and implanted medical devices. In addition, certain inductive coupling techniques have been reported to exhibit high power transfer efficiencies (on the order of 90%) for very short distances (1-3 cm). However, the efficiency of such techniques drops drastically for longer distances.
One type of wireless power transfer system employs a strongly coupled magnetic resonance (SCMR) method. A typical SCMR system employs an inductive transmitter loop and a spaced apart inductive receiver loop. Each loop resonates as substantially the same frequency. An alternating current source is used to excite the transmitter loop, which when resonating causes the receiver loop to resonate. The receiver loop is inductively coupled to a load and transfers power to the load as a result of its resonating.
Loop misalignment can result is a substantial decrease in efficiency. Conventional SCMR systems tend to be highly sensitive to the alignment between transmitter loop and receiver loop. The loops can be angularly misaligned, in which the loops exist on non-parallel planes. A greater angular difference in the planes results in lower power transfer efficiency. The loops may also be laterally misaligned, in which the loops may be parallel to each other but are on laterally spaced apart axes. Again, a greater distance between the axes results in a lower power transfer efficiency.
One approach to correcting SCMR's angular misalignment sensitivity employs tuning circuits. This method is generally not able to maintain high efficiency above 60° of misalignment. Also, tuning circuits add to the complexity of SCMR systems and they cannot compensate for large angular and radial misalignments as they cannot recover the lost flux density between transmitter and receiver. However, tuning circuits can be useful for compensating the effects of variable axial distance between the transmitter and the receiver.
Many digital devices require frequent data updating. One convenient time to update a digital device is during periods of non-use, such as when the device is being recharged.
Therefore, there is a need for a convenient wireless power transfer system that is efficient at longer distances.
Therefore, there is a need for a convenient wireless power transfer system that is efficient when the transmitter and the receiver are misaligned.
Therefore, there is a need for a convenient wireless power transfer system that facilitates both power transfer and data transfer simultaneously.